Immunoglobulins of the IgE class have been implicated as causing many of the symptoms of human allergy. This project examines the production of IgE in vitro by peripheral blood lymphocytes from allergic children with extremely high IgE levels. Specifically to be examined are the differences between non-allergic control subjects and allergic children in regard to IgE production. The peripheral blood lymphocytes will be fractionated into component subpopulations to determine whether there is a failure of regulatory cells residing in a subpopulation contributing to the excessive IgE production. The fractionation will be on the basis of cell surface receptors for sheep erythrocytes, for the Fc portions of IgG and IgM, and for theophylline and histamine. It is expected that these observations will provide insight into the basic defect in human allergy and suggest new and improved methods of therapy.